Update RGBApng2Palpng.c

Updating with my first stab at support for transparency in the ColorMap.  Removed support for SLD, as that's a thing of the past now.
GIBS-433 Simplified error messages
#17 Fixed time detection to use archive instead of cache location
GIBS-461 Added TIFF output support to mrfgen
#17 Refactored some code to bring back time updates and layer ordering
to WMTS GetCapabilities
#18 GIBS-362 Made georeference extents configurable
Merge branch 'master' of https://github.com/nasa-gibs/onearth into develop
#18 GIBS-362 Added option to mrfgen for resizing imagery with gdalwarp
#18 GIBS-362 Added XML schema definition file for mrfgen configuration
#19 GIBS-347 Initial legend image generation tool
#17 Updated file copy and print messages with oe_configure_layer
#19 GIBS-347 Modified generate_legend to handle various color map types
#19 GIBS-347 Legend generation updates to accomodate different use cases
#19 GIBS-347 Changed to vertical color bar
#19 GIBS-347 Fixed lines appearing in SVG color bar
#17 Fixed bug with time detection not skipping irrelevant files
#19 GIBS-347 Added colormap style property and modified legend
generation logic and formatting
#17 Added check to see if year directory contains data for time detect
19 GIBS-347 Moved units to start and end labels
 #19 GIBS-347 Converted classifications into legend items